Loading…

Application of local optical flow methods to high-velocity free-surface flows: Validation and application to stepped chutes

Experimental setup of ultra-high-speed video camera setup alongside the stepped spillway model and comparative experimental results in terms of interfacial velocity. [Display omitted] •Tests of two local optical flow techniques (Lucas-Kanade and Farneback).•Application to high-velocity air-water ski...

Full description

Saved in:
Bibliographic Details
Published in:Experimental thermal and fluid science 2018-01, Vol.90, p.186-199
Main Authors: Zhang, Gangfu, Chanson, Hubert
Format: Article
Language:English
Subjects:
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Experimental setup of ultra-high-speed video camera setup alongside the stepped spillway model and comparative experimental results in terms of interfacial velocity. [Display omitted] •Tests of two local optical flow techniques (Lucas-Kanade and Farneback).•Application to high-velocity air-water skimming flows above a stepped chute.•Simultaneous comparison with phase-detection probe measurements.•Close agreement in terms of flow patterns and void fraction.•Underestimation of bubble count rate and longitudinal velocity. The entrainment of air on a high-velocity spillway leads to a rapid bulking in flow depth and developments of complex flow patterns downstream of the inception point of aeration. This study examines the feasibility of two local optical flow techniques – the Lucas-Kanade method and the Farneback method – applied to high-velocity air-water skimming flows above a stepped chute. Such methods are not widely known to the multiphase flow community. Experimental studies were undertaken in a relatively large-size stepped spillway model. Validation test cases were performed using a synchronised ultra-high-speed camera and phase-detection probe setup. The optical flow technique detected changes in brightness due to reflectance difference associated with passages of air-water interfaces. The standard deviation of luminance correlates with void fraction and bubble count rate, and may be used asa predictor for uncertainties in optical flow estimation. The streamwise optical flow properties were in close agreement with those determined by the phase-detection probe next to the sidewall, with increasing differences for void fraction greater than 50% (C>0.5). In the sidewall region, however the bubble count rate and interfacial velocity distributions were underestimated compared to the channel centreline's interfacial properties. The tests demonstrated that the optical flow methods can provide useful qualitative and quantitative information on complex air-water flow patterns.
ISSN:0894-1777
1879-2286
DOI:10.1016/j.expthermflusci.2017.09.010